It is known that this type of shoe must reconcile a requirement of maximum flexibility so that it provides only minimal interference with foot movements, and a requirement that the sole be secured as effectively as possible to the sole of the foot, in general, to afford the user a good degree of stability, and, in the specific case of the cross country ski shoe, to allow precise control of the ski by the foot.
To offset the impossibility of ensuring effective securing of the sole to the sole of the foot through the intermediary of the substantially flexible upper of such a shoe, it has been proposed to dissociate the function of protection and insulation for the foot, which the upper ensures, and the function of securing the sole to the sole of the foot, which, in this case, is ensured by fasteners independent of the upper.
French Patent Application No. 85 12034 discloses a sport shoe, especially intended for cross country skiing, having a flexible upper and a sole as well as means to secure a foot in the shoe, with the securing means comprising the following:
first and second flexible fastening ties, each of which has on the one hand a first end attached to the inside of the shoe, in a lateral zone of the sole located respectively on a first or second side of the shoe and at the metatarsal level, and, on the other hand, successively, beginning with this first end, a first section running laterally along a foot housed in the shoe, at the metatarsal level, inside the shoe and independently of the upper, a second section to bypass the instep respectively up to the second or first side of the shoe, at the metatarsal level, inside the shoe and independently of the upper, with the second sections of the first and second flexible fastening ties being freely superposed, and a second end zone,
means for tightening or releasing the first and second flexible fastening ties by the mutual movable fastening of their second end zones, as desired.
In one embodiment of the shoe disclosed in the aforementioned patent application, the first and second flexible fastening ties have, between their second sections and their second end zones, mutually complementary third sections to bypass the foot by the rear, between a lower limit defined by the lower level of the lower attachment of the Achilles tendon to the calcaneum and an upper limit level defined by the lower level of the malleoli, so that the tightening of the first and second flexible fastenings does not impede the extension movements of the foot.
These arrangements are especially effective when it comes to preventing the front part of the foot from pivoting on the sole, which is to be avoided especially in cross country skiing; however, these arrangements allow a certain degree of freedom for the heel with respect to the sole, against which the foot is fastened only at the metatarsal level.
However, for certain sports such as golf, for example, it is indispensable for the whole foot to be perfectly immobilized with respect to the sole, to provide the user with the highest possible degree of stability, i.e., a possibility of precisely controlling his position and movements; such a possibility is also desirable in other sports, and even in cross country skiing.